Commonly, a railroad locomotive in a consist travels between stations unattended. If the engine of such a locomotive should, for any reason, shut down, the heat in the cooling system will dissipate rapidly. In cases where the train is traveling at high speed and ambient temperature is well below zero, the coolant will freeze very quickly, and the engine and/or components of the cooling system can be severely damaged. Because of this possibility, it has been proposed to equip locomotives with apparatus for automatically draining coolant from the cooling system under conditions which may cause freeze-ups. One kind of apparatus which has been employed comprises a poppet type valve which is arranged to drain coolant from the lowest region of the system and whose movable head is spring biased against its seat. The head is unseated either by a solenoid, or by a piston to which compressed air is selectively delivered by a separate solenoid valve. In either case, the solenoid is energized by an electrical circuit which includes a contact of the No Voltage Relay (NVR) and a temperature responsive switch. While this kind of apparatus theoretically solves the problem of preventing freezing of the coolant, from the practical standpoint it has proven deficient. Two of the most serious difficulties which I have encountered are leakage at the seat of the drain valve, and corrosion of the head-carrying stem which prevents full opening as well as re-seating of the head. In addition, since the apparatus automatically re-sets, i.e., closes the drain valve, when the temperature rises above the freezing level, or the electrical circuit is disabled, an empty cooling system can be refilled inadvertently at times when this is imprudent. Finally, since the apparatus has no provision for effecting manual draining, additional equipment must be provided for that purpose.
Another known type of automatic drain apparatus employs a drain plug which is released by a pressure surge in the coolant produced by an explosive squib. The squib is detonated automatically by an electrical circuit in response to the occurrence of freezing conditions. In my experience, this kind of drain device is not satisfactory, first, because misfiring is not uncommon, and second, because it cannot be reset, but must be removed from the locomotive and returned to the manufacturer for recharging after each use. Furthermore, the device obviously is not suitable for manual draining operations.